Normal breast epithelial cells are known to exert an apoptotic effect on breast cancer cells, resulting in a potential paracrine inhibition of breast tumor development. Here, we have purified and characterized the apoptosis-inducing factors secreted by normal breast epithelial cells. Conditioned medium was concentrated by ultrafiltration and separated on reverse phase Sep-pak C18 and HPLC. The proapoptotic activity of eluted fractions were tested on MCF-7 breast cancer cells and nanoLC-nanoESI-MS/MS allowed the identification of insulin-like growth factor binding protein-3 (IGFBP-3) and maspin as the proapoptotic factors produced by normal breast epithelial cells. Western blot analysis of conditioned media confirmed the specific secretion of IGFBP-3 and maspin by normal cells but not by breast cancer cells. Immunodepletion of IGFBP-3 and maspin completely abolished the normal cells-induced apoptosis of cancer cells and recombinant proteins reproduced the effect of normal cell-conditioned medium on apoptosis of breast cancer cells. Together, our results indicated that normal breast epithelial cells can induce apoptosis of breast cancer cells through IGFBP-3 and maspin. These findings provide a molecular hypothesis for the long time observed inhibitory effect of normal surrounding cells on breast cancer development.